.cfg file resets itself instantly

[Semper Fi or Die]

Hello, so my Stainless Steel started for reasons unknown to me starting up in Windowed Mode. I thought no problem, let's go on the .cfg file and change it.

The problem: As soon as I open SS (not that it matters but 6.4) the cfg file is reset, in other words, my changes are undone automatically, forcing me to play SS on Windowed Mode.

The only thing I could think of that I did that affected my SS running in fullscreen would be running vanilla Medieval 2, but that runs fullscreen without any issues.

Thanks in advance.

[Losthief]

click on properties untick read-only, make edit, save, re-tick read only.